PARTURITION. 349 



The internal organs, i.e. the uterus and vagina in the female, and 

 vasa deferentia, seminal vesicles, and uterus masculinus in the male, 

 differ from the external organs in receiving no efferent nerve fibres 

 from the sacral nerves, as has been pointed out by Langley and 

 Anderson. They are supplied with fibres which pass out through the 

 anterior roots of the third, fourth, and fifth lumbar nerves (in the 

 rabbit and cat), and run through the sympathetic to the inferior 

 mesenteric ganglia, whence they proceed by the hypogastric nerves. 

 On stimulating these fibres, two effects are produced on the uterus and 

 vagina, namely, a contraction of the small arteries, leading to pallor 

 of the organs, and a strong contraction of the muscular coats. In the 

 vagina, the contraction can usually be seen to start from one end and 

 spread to the other. The whole then remains for a time in a state of 

 powerful tonic contraction, which affects both longitudinal as well as 

 circular muscles. In the male, stimulation of these nerves excites 

 strong contraction of the whole musculature of the vasa deferentia and 

 seminal vesicles, which may be strong enough to cause emission of 

 semen from the penis. Here again both sets of muscular fibres are 

 involved. These effects on the uterus and seminal vesicles are not 

 abolished by injection of atr opine. 



The course of the sensory fibres from the generative organs to the 

 lumbo-sacral cord has not yet been fully made out, but it seems 

 probable that it corresponds to the course taken by the efferent fibres. 



An accessory genital muscle, the retractor penis, which is found in the 

 dog, cat, horse, donkey, hedgehog (not in the rabbit or man), presents con- 

 siderable physiological interest. It was first described by Eckhard as the 

 Afterrutlienband, and consists of a thin band of longitudinally arranged 

 unstriated muscle (15 to 20 cms. long in a spaniel weighing about 15 kilos.), 1 

 which is inserted at the attachment of the prepuce, and is continued backwards 

 in a sheath of connective tissue to the bulb, when it divides into two slips 

 which pass on either side of the anus. A few striated fibres are found in the 

 back part of this muscle, derived from the external sphincter of the anus and 

 the bulbo-cavernosus muscles. 



This muscle is extremely sensitive to changes of temperature, and is at 

 the same time very tenacious of life. Thus it may be cut out of the body and 

 kept in serum or blood, in a cool place, for two days. At the end of this time 

 it will, on warming, relax, and enter into spontaneous rhythmic contractions. 

 At about 40 C. the muscle is quite flaccid. On cooling slightly (to 35) it 

 will shorten, and at the same time may enter into slow rhythmic contractions. 

 If cooled to 15 C. the muscle will contract to about a quarter of its previous 

 length. The same shortening may be produced on exciting the muscle with 

 strong interrupted currents. 



The muscle is innervated from two sources, the two nerves having 

 antagonistic actions. The motor fibres to the muscle are derived from the 

 lumbar sympathetic (i.e. the upper set of nerve roots), and run to the muscle 

 in the internal pudic nerve. The pelvic nerves, on the other hand, carry 

 inhibitory impulses to the muscle, thus enabling the concomitant vascular 

 dilatation to take effect in producing erection of the penis. 



Parturition. During pregnancy, marked changes take place in all 

 the generative organs, the most important and striking being those 

 affecting the uterus. This organ undergoes an enormous hypertrophy 

 involving all its tissues, so that, whereas in a virgin the uterus is about 



1 Langley and Anderson, loc. cit., p. 88. 



